Senate Republicans backed by a group of rural-state Democrats scuttled the most far-reaching gun control legislation in two decades Wednesday, rejecting tighter background checks for buyers and a ban on assault weapons.

“This effort isn’t over,” President Barack Obama vowed at the White House moments after the defeat on one of his top domestic priorities. He said opponents of the legislation in both parties “caved to the pressure” of special interests.

As he spoke, the president was surrounded by relatives of victims of last winter’s school massacre in Newtown, Conn., where a gunman killed 20 elementary school children and six staff members at Sandy Hook Elementary School.

A ban on high-capacity ammunition magazines also fell in a series of showdown votes.

A bid to loosen restrictions on concealed weapons carried across state lines was rejected as well.

That last vote marked a rare defeat for the National Rifle Association on a day it generally triumphed over Obama, gun control advocates and many of the individuals whose lives have been affected by mass shootings in Connecticut and elsewhere.

Some of them watched from the spectator galleries above the Senate floor. “Shame on you,” shouted one, Patricia Maisch, who was present two years ago when a gunman in Tucson, Ariz., killed six and wounded 13 others, including former Rep. Gabrielle Giffords.

Vice President Joe Biden gaveled the Senate back into order after the breach of decorum.

Gun control advocates, including Obama, had voiced high hopes for significant action after the Newtown shootings. But the lineup of possible legislation gradually dwindled to a focus on background checks, and in the end even that could not win Senate passage. Chances in the Republican-controlled House had seemed even slimmer.

By agreement of Senate leaders, a 60-vote majority was required for approval of any of the provisions brought to a vote.

The vote on the background check was 54-46, well short of the 60 votes needed to advance the legislation. Forty-one Republicans and five Democrats voted to reject the plan.

The proposed ban on assault weapons commanded 40 votes; the bid to block sales of high-capacity ammunition clips drew 46.

The NRA-backed proposal on concealed carry permits got 57 votes.

In the hours before the key vote on background checks, Sen. Joe Manchin, D-W.Va., accused the National Rifle Association of making false claims about the expansion of background checks that he and Sen. Pat Toomey, R-Pa., were backing.

“Where I come from in West Virginia, I don’t know how to put the words any plainer than this: That is a lie. That is simply a lie,” he said, accusing the organization of telling its supporters that friends, neighbors and some family members would need federal permission to transfer ownership of firearms to one another.

The NRA did not respond immediately to the charge, but issued a statement after the vote that restated the claim. The proposal “would have criminalized certain private transfers of firearms between honest citizens, requiring lifelong friends, neighbors and some family members to get federal government permission to exercise a fundamental right or face prosecution,” said a statement from Chris Cox, a top lobbyist for the group.

Other opponents argued that the Manchin-Toomey approach simply wouldn’t work.

“We should not further strain the existing broken system by expanding the use of an incomplete database to more transactions,” said Sen. Charles Grassley, R-Iowa. “We should fix the existing system.”

Grassley and Sens. Lindsey Graham, R-S.C., and Ted Cruz, R-Texas, offered an alternative that would increase the number of mental health records entered into the federal background check database.

Even before the votes, the administration signaled that the day’s events would not be the last word on an issue that Democratic leaders shied away from for nearly two decades until Obama picked up on it after the Newtown shootings.

Democratic aides said in advance the issue would be brought back to the Senate in the future, giving gun control supporters more time to win over converts to change the outcome.

Obama, standing near Giffords and relatives of other shooting victims, said at the White House that public opinion was strongly behind expanded background checks. Despite that, opponents of the legislation were “worried that the gun lobby would spend a lot of money” at the next election, he said.

“So all in all, this was a pretty shameful day for Washington,” he added.

The day’s key test concerned the background checks, designed to prevent criminals and the seriously mentally ill from purchasing firearms. Under current law, checks are required only when guns are purchased from federally licensed firearms dealers. The proposal by Manchin and Toomey called for extending the requirement to other sales at gun shows and on the Internet.

On the vote, Democratic Sens. Mark Begich of Alaska and Max Baucus of Montana joined Pryor and Heitkamp in voting against the proposal. Senate Majority Leader Harry Reid, a supporter of the plan, switched his vote to the prevailing “no” side to permit him to call for a revote in the future.

Begich, Pryor and Baucus are all seeking re-election next year. In an indication of the intensity of the feelings on the issue, the Progressive Change Campaign Committee, a liberal group, swiftly announced it would seek to defeat them in 2014.

Among Republicans, Sens. Susan Collins of Maine, Mark Kirk of Illinois, John McCain of Arizona and Toomey sided with Democrats.

Numerous polls in recent months have shown support for enhanced gun control measures, including background checks, though it may be weakening.

An Associated Press-GfK poll this month showed that 49 percent of Americans support stricter gun laws, down from 58 percent in January. In that recent survey, 38 percent said they want the laws to remain the same and 10 percent want them eased.